This invention relates to a magnetic core for use in an electronic apparatus and to a magnetic device comprising the magnetic core and a winding wound around the magnetic core.
A typical magnetic device such as a choke coil or a transformer comprises a magnetic core such as a drum-shaped core block made of a magnetic material and a winding wound around the magnetic core. In order to achieve the reduction in size and weight of the magnetic device, it is effective to reduce the volume of the magnetic core, as known in the art. However, the magnetic core reduced in size is readily saturated in magnetization. As a result, an acceptable current level is inevitably decreased.
In order to solve the above-mentioned problem, use has been made of an approach of forming a gap at a part of the magnetic core to increase a magnetic resistance so that the acceptable current level is prevented from being decreased. This approach is, however, disadvantageous because a magnetic inductance as an inherent characteristic value of the magnetic device is reduced.
On the other hand, Japanese Examined Utility Model Publication No. S43-3771 (JP 43-3771 Y) discloses a flyback transformer utilizing another approach. Referring to FIG. 1, description will hereinafter be made of a magnetic device corresponding to the flyback transformer. The magnetic device illustrated in FIG. 1 comprises a magnetic core 1 and a winding 2 wound around the magnetic core 1. The magnetic core 1 has a winding core portion 3 having an outer peripheral surface having a circular cylindrical shape to receive the winding 2, and a pair of flange portions 4 and 5 integrally coupled to opposite ends of the winding core portion 3 in its axial direction respectively. The magnetic core 1 has an axial one end provided with a disk-shaped permanent magnet 6 attached thereto. The permanent magnet 6 is magnetized in its thickness direction, i.e., in an axial direction of the magnetic core 1. In this manner, the magnetic core 1 is applied with a DC magnetic bias by the permanent magnet 6 in order to prevent magnetic saturation of the magnetic core 1.
Referring to FIG. 2, description will be made of the magnetic bias in the magnetic device illustrated in FIG. 1. The permanent magnet 6 generates a DC magnetic field 7. When the winding 2 is energized, an AC magnetic field 8 is generated. Since the permanent magnet 6 has a disk shape, the magnetic bias applied by the permanent magnet 6 is concentrated to the winding core portion 3. On the other hand, the flange portions 4 and 5 are hardly applied with the magnetic bias. Therefore, the above-mentioned approach is insufficient to prevent the decrease in saturation flux density resulting from the reduction in size of the magnetic core.
It is therefore an object of this invention to provide a magnetic core capable of effectively preventing, by a magnetic bias, the decrease in saturation flux density resulting from the reduction in size of the magnetic core.
It is another object of this invention to provide a magnetic core of the type mentioned above, which can be reduced in cost, size, and weight.
It is still another object of this invention to provide a magnetic device comprising the above-mentioned magnetic core.
Other objects of the present invention will become clear as the description proceeds.
According to the present invention, there is provided a magnetic core which comprises a winding core portion having a center axis and an outer peripheral surface which surrounds said center axis to have a first distance therebetween, and a flange portion coupled to the winding core portion and protruding outward the winding core portion in a radial direction perpendicular to the center axis. The flange portion has a permanent magnet apart from the center axis by a second distance greater than the first distance.
According to the present invention, there is provided a magnetic device which comprises the magnetic core and a winding wound around the winding core portion of the magnetic core.